This invention relates to an improved system for post-detection processing of information in radar receivers.
Heretofore, a single channel medium PRF pulse doppler radar receiver was proposed that effectively prevented sidelobe return signals from being displayed as "ghost" or "false" targets. In such system, the received signal data is preliminarily processed by a filter bank and a CFAR (constant false alarm) threshold circuit to remove main-beam clutter and area sidelobe clutter returns. The preliminarily processed data is then temporarily stored, as two parallel correlations are performed on a range call by range cell basis to identify range cells which contain discrete sidelobe clutter return signals. One of the parallel correlations is performed on the data after it is passed through a sensitivity time control threshold circuit, and the other parallel correlation is performed on the raw data. The outputs of the parallel correlators are then compared. The identified range cell correlations in the raw data correlator are compared with corresponding range cells of the sensitivity time control correlations to idenfity range cell numbers which contain discrete sidelobe clutter return signals. Identified range cell numbers are then blanked from the raw data before it is correlated for a third time. The output of the third correlator identifies the true target return signals and the corresponding unambiguous range thereof.
Although such a system, which is described in detail in U.S. Pat. No. 4,095,222 entitled "Post-Detection STC In A medium PRF Pulse Dopper Radar" issued June 13, 1978, to Mooney, Jr., operates effectively and satisfactorily, the operation of the ABC Correlators degrades when the radar is operated in a dense target environment with mutiple targets visible during the processing dwell. Large numbers of range ghosts are generated by targets cross correlating with one another. Some of these ghosts are removed by (A and not B) blanking when they are produced at short ranges (within the STC range) by targets out at long ranges. Unfortunately, since the blanking is performed ambiguously in range, the real targets that produce these ghosts are also blanked out. The result is that significant numbers of range ghosts are reported while true targets with ample S/N are blanked.